Conductive foams are currently manufactured for purposes other than induction heating. These foams are currently used in conductive grounding and static electrical dissipation applications, principally used in electronic or microchip fabrication facilities. Conductive foams direct static charge away from precious electro-sensitive parts. Static-dissipative packaging foam insulates, structurally protects and electrically protects sensitive electronic parts. These markets are limited in size and thus current production of static and electrically dissipative foam is limited. The foams are expensive because of limited demand. New markets that increase the demand for such foams will drive compounding costs down as the cost of susceptor material is negligible.
The production of thermoplastic closed-cell foam sheet and laminates and their industrial conversion into manufactured parts such as insoles and cushioning are time consuming processes. The rate limiting steps are 1) the time required to initially produce the foam, 2) the time required to heat the foam and 3) the cure time in the mold. A typical industrial foam conversion system involves standard ovens or infrared (IR) preheating of sheet foam to approach melting temperature. Although IR has improved speed of heating, it still takes 3060 seconds to uniformly heat most xc2xcxe2x80x3 thick thermoplastic foams. The principal problem of heating foams using standard technology is due to the structural insulative capacity of foam. Such-heating systems require that the air trapped within the foam be heated as well as the base polymer. Thus, the heated foam absorbs and retains higher levels of heat to approach melting temperatures. Cooling thoroughly-heated, converted foams takes significant time also due to the insulative properties of the foam. A typical press used for insole technology will take 30-120 seconds to cool the foam depending on thickness. Such heating and cooling times do not lend themselves to automation, thus virtually all insoles manufactured in the world are manufactured using semi-automated or manual processes.
The invention resolves the above stated problems by provision of a material that is inherently susceptible (will soften by heating from the inside out via magnetic induction) or has susceptible inclusions as layers or particles intermixed with a non-susceptible matrix for similar heat softening via magnetic induction. The magnetic induction can be provided via microwave, electromagnetic coils and other known induction forms.
The material, when softened, is sufficiently malleable to conform to a molding impression provided by a human body part (e.g., hand, knee, foot) or other complex curvature object and to take a permanent set conforming to such curvature as the material cools.
The material has sufficient thermal insulation characteristic to be heat softened internally and substantially cooler to the touch on the outside to enable many of the uses described below.
Another aspect of the invention includes the use of susceptor particles, mixed with resin, to accelerate polymerization of the resin by inductively heating the susceptor particles. Further, susceptor particles may also be incorporated in resins during polymeric molding operations. As the polymer is being cast, the susceptor particles are inductively heated to drive polymerization without need to heat the mold.